1. Field of the Invention
This invention relates to a dental articulator used for completely reproducing human jaw movement, especially articulation, in producing dental prostheses for defective or missing teeth.
2. Description of the Prior Art
Reproduction of mandibular movement is indispensable to production of dental prostheses for enabling good mastication. Interocclusal movement shows highly noticeable differences among individuals. Thus, a dental articulator capable of completely reproducing the mandibular movement of the jaw of each individual is desired, and accordingly, there have been so far proposed a variety of dental articulators for this purpose.
As one of the dental articulators, there is an arcon-type full-adjustable articulator. The arcon type denotes a structure, which is provided at its mandible portion with a condylar sphere similarly to a living subject, and at its maxilla portion with condyle path regulation. The full-adjustable articulator comprises a regulating mechanism having a function of detecting mandibular movement in a form of three-dimensional movement of the jaw to effect three-dimensional regulation for the entire movement.
In Japanese Patent No. 2866084 (Japanese Patent Application Publication No. HEI 11-028217), the inventors of the present invention disclosed an arcon-type xe2x80x9ccompletely reproducible articulatorxe2x80x9d capable of perfect reproduction of mandibular movement. The articulator disclosed in this Japanese publication will be discussed, upon explaining an ordinary technique in relation to the articulator.
First, terminology for describing an occlusion will be briefly defined. In dentistry, the front, side and plane in a general sense are expressed in terms of xe2x80x9cfrontal planexe2x80x9d, xe2x80x9csagittal planexe2x80x9d and xe2x80x9cocclusal planexe2x80x9d, respectively. In general, the side toward which mandibular movement is directed is termed the xe2x80x9cworking sidexe2x80x9d, and the opposite side is termed the xe2x80x9cbalancing sidexe2x80x9d or xe2x80x9cnon-working sidexe2x80x9d. Of the maxilla and mandible, which constitute the jaw, the mandible is movable and restrained in movement via configuration of the glenoid fossae accommodating right and left xe2x80x9ccondyle headsxe2x80x9d. The mandible moves in five directions, i.e. protrusive, lateral (leftward), lateral (rightward), posterior and vertical directions. A center of a condylar point is termed xe2x80x9ccondylar pointxe2x80x9d, a line connecting centers of right and left condyle heads is termed xe2x80x9ccondylar axisxe2x80x9d, and locus along which the condylar point moves along the glenoid fossae is termed xe2x80x9ccondyle pathxe2x80x9d.
The conventional full-adjustable articulators also have various types of contrivances for reproducing the mandibular movement, which are common in principle.
First, jaw movement to be reproduced is fulfilled by the mandibular movement made in the five directions as touched upon above. However, all five-directional mandibular movements, may be practically ruled out of the movements of the conventional articulators. That is, movement of the condylar points in the protrusive, leftward and rightward directions will suffice for reproducing the jaw movement. With respect to the lateral movement of the jaws, when the mandible moves rightward, the right condyle head works as the working side and the left condyle head works as the balancing side. The reverse is also true when the mandible moves Leftward. Thus, the jaw movement to be reproduced must vary according to the movement of each condyle head, which is performed in different manner in moving the mandible rightward or leftward.
That is to say, the jaw movement at the time of the protrusive motion of the condyle heads and the lateral motions of the right and left condyle heads when the respective condyle heads work as the working side or balancing side may be accurately reproduced. In other words, it may be required to reproduce only the protrusive movements of the right and left condyle heads and the lateral movements of the condyle head (working condyle head) and condyle head (balancing condyle head).
There has been a method for reproducing movement of the condyle heads noted above, in which a three-dimensional reproduction of the movement is effected by combining movements of the jaw in an internal-external, upward-downward and anteroposterior directions. With a dental articulator, jaw movement has been recognized by bringing a plate member called a xe2x80x9cregulation platexe2x80x9d in touch with the condyle heads so as to permit the condyle heads to move along the regulation plate, and varying an angle (gradient) of the regulation plate to derive a direction in which the regulation plate moves relative to condyle heads. Hence, internal-external, upward-downward and anteroposterior regulation plates are provided for each condyle head in order to regulate movements of the condyle head, so that the condyle heads are guided in composite directions in which the regulation plates are regulated.
In a common articulator, a vertical regulation plate is called a xe2x80x9csagittal condylar path inclination platexe2x80x9d, a mesio-lateral regulation plate is called a xe2x80x9cBennett platexe2x80x9d, and an anteroposterior regulation plate is called a xe2x80x9crear wallxe2x80x9d.
Next, a regulating method will be described in detail. At the time of protrusive movement of a jaw, both condyle heads move in an anterior-downward direction during the protrusive movement, thereby to be restrained in a vertical direction. During lateral movement of the jaw, the working condyle head moves slightly, but the balancing condyle head largely moves inwardly in an anterior-downward direction. Consequently, the balancing condyle head is restrained in vertical and lateral directions, and simultaneously, the working condyle head is restrained in vertical and anteroposterior directions, while being thrust outwardly.
What does matter at this point is usage of vertical regulation for reproducing three sets of vertical components of the protrusive movement, right lateral movement and left lateral movement. To be specific, the sagittal condylar path inclination plate used for vertical regulation corresponds to these movements made in three directions, but the vertical components of the movements in the three directions varies relative to each other with the direction in which the jaw moves. Thus, in a case that the mandible is regulated in its right lateral movement and successively in its left lateral movement, the right condyle head first works as the working condyle and successively as the balancing condyle. At that time, it is necessary to readjust an angle of the sagittal condylar path inclination plate. Therefore, work required for the regulation disadvantageously requires much time and labor and proves to be troublesome.
To overcome the unfavorable problems described above, there has been adopted a method in which a rotary inclination mechanism called a xe2x80x9cFischer slidexe2x80x9d is attached to the sagittal condylar path inclination plate. FIG. 15 shows a conventional articulator adopting a method using a xe2x80x9cFischer slidexe2x80x9d. As shown in FIG. 15, one sagittal condylar path inclination plate 522 is provided with an inclination rotatable about an intercondylar axis (A) and an inclination (of the Fischer slide) rotatable about a sagittal condylar path inclination axis (C), thereby to possess two inclination angles, so that the sagittal condylar path inclination plate 522 can be restrained in two directions of vertical movement with one regulation plate. However, this conventional method capable of reproducing only two of the movements made in three directions required for vertical regulation could not completely reproduce the desired mandibular movement. In FIG. 15, reference numeral 513 denotes the condyle head, 521 denotes the Bennett plate (angular regulation plate rotatable about the axis B), and 523 denotes the rear wall (angular regulation plate rotatable about the axis R).
To overcome the disadvantage suffered by the conventional articulator, the inventor of this invention proposed in Japanese Patent No. 2866084 an improved articulator capable of completely reproducing the mandibular movement.
To be more specific, a xe2x80x9cBennett lift mechanismxe2x80x9d disclosed in Japanese Patent No. 2866084 enables vertical regulation of the working condyle, and consequently enables three directional movements of the condyle heads. The Bennett lift mechanism was invented by the inventor of this invention and is explained in detail in Japanese Patent No. 2866084.
Operation of the articulator disclosed in Japanese Patent No. 2866084 is schematically illustrated in FIG. 16. As illustrated, a proposed articulator 1m has a structure for reproducing jaw movement made with moving the maxilla. A base 102m is provided on a mandibular frame 10m for a mandibular cast 2, and is provided at both its side ends with condylar sphere members 13m in imitation of the condyle heads. A condyle box 14m constituted by a plurality of regulation plates is brought into contact with the condylar sphere members 13m, so that a maxillar frame 11m for supporting a maxillar cast 3 is guided through the condyle box 14m. Therefore, rightward movement of the mandibular cast is fulfilled by moving the maxillar cast leftward, and leftward movement of the mandibular cast is fulfilled by moving the maxillar cast rightward. Thus, relative movement of the mandible and maxilla can be reproduced in this manner.
The proposed articulator 1m is provided with a Bennett lift mechanism 15m independent of the condyle box 14m, in such a state that a cam 50m formed on a rear of the base 102m comes into contact with a pin 51m. 
The aforementioned Bennett lift mechanism 15m of the proposed articulator is used exclusively for regulating vertical movement of the working condylar sphere member 13m. That is, the Bennett lift mechanism 15m on the working side is operated when the balancing condylar sphere member 13m moves inwardly in an anterior-downward direction by virtue of the vertical regulation plate (sagittal condylar path inclination plate) and the mesio-lateral regulation plate (Bennett plate). At this time, the working condylar sphere member 13m is apart from the sagittal condylar path inclination plate, and simultaneously, restrained in vertical movement by the Bennett lift mechanism 15m. The sagittal condylar path inclination plate contributes not only to protrusive movement of the condylar sphere member, but also to lateral movement of the balancing condylar sphere member 13m, and consequently restrains the forward and balancing movements of the condylar sphere members through agency of the Fischer slide.
Accordingly, the articulator 1m makes it possible to reproduce all jaw movements in protrusive, balancing and working states, which require vertical restriction in movement, in addition to the Bennett lift mechanism 15m. 
However, the Bennett lift mechanism 15m disclosed in Japanese Patent No. 2866084 (hereinafter referred to as a xe2x80x9cprior art Bennett lift mechanismxe2x80x9d) has disadvantageously entailed a problem such as a possible malfunction of the maxillar cast 3 and mandibular cast 2 at a time of opening and closing.
This is attributable to the cam 50m formed on the rear of the base 102m colliding with the pin 51 mounted on the maxillar frame in opening or closing the maxillar cast 3 and mandibular cast 2, which consequently causes deviation of a rotating axis of the opening and closing movements from an intercondylar axis toward the rear of the base 102m. Although a line (intercondylar axis) connecting the right and left condyle heads should serve as a rotational center, it is shifted to a line connecting right and left Bennett lift mechanisms 15m in practice. As a result, rotation is made about an axis carrying fulcrum 52m at which the pin 51 comes into contact with the cam 50m, and consequently detaches the condylar sphere 13m from the condyle box 14m. Besides, since the pin 51m of the Bennett lift mechanism 15m comes into contact with an upper surface of the cam 50m, the fulcrum 52m is slid on the surface when opening the maxillar and mandibular casts, and consequently causes further deviation of the rotational axis. As a result, the maxillar cast and mandibular cast disadvantageously get out of position and lack stability. The work of confirming occlusion when opening and closing the maxillar and mandibular casts is of great importance from the point of view of usage of the articulator. In spite of the needs for high reliability and reproducibility of the articulator, the proposed articulator has suffered a disadvantage in that deviation of a central axis as noted above renders the articulator considerably inconvenient to operate.
The proposed articulator is further disadvantageous in that there is a structural limit in the angle at which the regulation plates of the condyle box 14m are restrained. That is, the regulation plates such as the sagittal condylar path inclination plate, Bennett plate and rear wall, which constitute the condyle box 14m, collide with one another when they change in gradient, and thus restrain angular movements of the regulation plates.
An object of the present invention is to provide an articulator capable of completely and faithfully reproducing movements of a mandibular cast and maxillar cast by analogy of occlusion of a human.
Another object of the present invention is to provide an articulator capable of tight and rigid hinge movement in opening and closing the maxillar and mandibular casts in a centric occlusion position.
Still another object of the present invention is to provide an articulator capable of lightening restraint on angular movements of regulation plates, which is possibly caused by collision of the regulation plates.
To attain the objects described above according to the present invention, there is provided a completely reproducible articulator comprising a maxillar frame for supporting a maxillar cast, a mandibular frame for supporting a mandibular cast, a pair of condylar spheres placed between the mandibular and maxillar casts, condyle boxes placed between the mandibular and maxillar casts, and Bennett lift mechanisms disposed on a base axis connecting the condylar spheres independent of the condyle boxes.
The mandibular and maxillar casts are movable laterally. During lateral movement of the mandibular and maxillar casts, one of the condylar spheres serves as a working condylar sphere, and the other serves as a balancing condylar sphere. With the Bennett lift mechanisms, the working condylar sphere is independently restrained in its vertical movement during lateral movement of the mandibular and maxillar casts. The Bennett lift mechanisms disposed on the base axis (equivalent to the condylar axis) rotate about the base axis when opening and closing the mandibular and maxillar casts in a centric occlusion position.
There may further be disposed a pair of second condylar spheres on the base axis, so that vertical movement thereof can be restrained by the Bennett lift mechanisms, thus reproducing movements of the working side condyle.
An axis fixing mechanism may be provided for coinciding the rotational center with the base axis while opening and closing the mandibular and maxillar casts in the centric occlusion position, thus to overcome instability in which the mandibular and maxillar casts are easy to separate. Accordingly, the opening and closing of the mandibular and maxillar casts can be stably performed repeatedly while retaining the rotational axis on the base axis, to consequently improve reliability in operation.
The axis fixing mechanism may be provided with an engaging member for elastically connecting the mandibular frame and the maxillar frame, so that the mandibular and maxillar casts are caught with this engaging member so as to be prevented from being separated. As a result, reliable opening and closing movements about the base axis can be performed.
Or, the axis fixing mechanism may be provided with an axial rod and an engaging portion for elastically connecting the mandibular cast and the maxillar cast, so that the mandibular and maxillar casts are caught by the axial rod and engaging portion so as to be prevented from being separated from each other. As a result, the reliable opening and closing movements about the base axis can be performed.
Independent of the condyle box, anteroposterior regulation plates may be disposed for regulating movement in the anteroposterior direction relative to the working condylar sphere, so as to be prevented from colliding with each other in the condyle box. As a result, limits in which the regulation plates are movable can be made large.
Or, inner and outer regulation plates for regulating lateral movement of the working condylar sphere may be disposed independent of the condyle box, so as to be prevented from colliding with each other in the condyle box. As a result, limits in which the regulation plates are movable can be made large.
Other and further objects of this invention will become obvious upon an understanding of the illustrative embodiments about to be described, or will be indicated in the appended claims, and various advantages not referred to herein will occur to one skilled in the art upon employment of the invention in practice.